In recent years, an increase in food poisoning caused by infection with microorganisms such as Escherichia coli and Salmonella enterica has been a problem. A major cause of this problem is a washing failure. Therefore, it is necessary to conduct a cleanliness inspection in a food-processing factory.
As such inspection, a method in which cleanliness is analyzed by measuring ATP (adenosine triphosphate) or AMP (adenosine monophosphate) has been put into practical use in recent years. ATP and AMP are known as necessary components for energy metabolism in various organisms. Therefore, it is considered that the amount of ATP or AMP has a correlation to the amount derived from the microorganisms and food present therein. Thus, by measuring ATP or AMP in an objective region, the extent of microorganisms and food residues remaining in the region can be analyzed. Accordingly, cleanliness can be evaluated.
As a tool for detecting AMP, for example, a nucleic acid element obtained by linking a DNA aptamer that specifically binds to AMP with DNA (hereinafter merely referred to as DNAzyme) that exerts peroxidase activity has been reported (Non-Patent Document 1). The structure of this nucleic acid element is controlled so that a catalytic ability of DNAzyme is inhibited by self-association of an aptamer with the DNAzyme in the absence of AMP, and the self-association is released by a binding of AMP to the aptamer in the presence of AMP, thereby exerting the catalytic ability of the DNAzyme. Therefore, for example, when AMP is present, a peroxidase reaction occurs by DNAzyme exerting a catalytic ability. Thus, the amount of AMP can be measured indirectly by meaning the reaction. On the other hand, when AMP is not present, the catalytic ability of DNAzyme is not exerted. Thus, the peroxidase reaction does not occur. However, such nucleic acid element is required to further improve the sensitivity, the ease of handling, and the like in order to put the nucleic acid element into practical use. Such requirement is applied not only to AMP but also ATP and the other targets.